The present invention relates to a low dielectric loss tangent resin composition used for insulating materials of electrical parts having low dielectric loss for corresponding to high frequency signals, cured products of the composition and electrical pats using the same.
In recent years, the signal band of information communication apparatuses, such as PHS and portable telephones, and the CPU clock time of computers have reached the GHz band, and the trend toward higher frequency is increasingly strong.
The dielectric loss of an electric signal is proportional to the square root of dielectric constant of the insulating material constituting the circuit and to the product of the dielectric loss tangent and the frequency of the signal used. Therefore, the higher the frequency of the signal, the larger the dielectric loss. Since dielectric loss causes attenuation of electric signals to lower the reliability of the signals, it has been necessary to select as an insulator a material which has a low dielectric constant and low dielectric loss tangent.
For obtaining an insulating material having a low dielectric constant and low dielectric loss tangent, it is effective to remove polar groups in its structure, and there have been proposed fluororesin, curable polyolefin, cyanate ester resin, curable polyphenylene oxide, allyl-modified polyphenylene ether and polyether imide modified with divinylbenzene or divinylnaphthalene.
Fluororesins typically represented by polytetrafluoroethylene (PTFE) have both a low dielectric constant and a low dielectric loss tangent and are used as materials for substrates which deal with high frequency signals. However, since PTFE is a thermoplastic resin, it undergoes large expansion and shrinkage in molding and processing and hence is a material not easy to handle.
A number of proposals have been made to impart crosslinkability or solubility to fluororesin. However, materials thus obtained are generally expensive, and many of them are not comparable to fluororesin in characteristic properties.
On the other hand, various studies have been made to obtain non-fluorine type resins of low dielectric constant and low dielectric loss tangent which are soluble in organic solvents and are easy to handle.
For example, there have been disclosed a product obtained by impregnating glass cloth with a diene-type polymer, such as polybutadiene, followed by curing with a peroxide (JP-A-8-208856), a cyclic polyolefin obtained by introducing an epoxy group into a norbornene-type addition polymer thereby to impart curability to the product (JP-A-10-158337) and products obtained by heating cyanate ester, diene-type polymer and epoxy resin to reach the B-stage (JP-A-11-124,491).
There have been further disclosed many example, which include a modified resin comprising polyphenylene oxide, diene-type polymer and triallyl isocyanate (JP-A-9-118759), a resin composition comprising allyl-modified polyphenylene ether, triallyl isocyanate, etc. (JP-A-9-246429), an alloyed products of polyether imide with styrene and divinylbenzene and/or divinylnaphthalene (JP-A-5-156159), a product synthesized by the Williamson""s reaction from a dihydroxy compound and chloromethylstyrene, e.g., a resin composition comprising hydroquinone bis(vinylbenzyl) ether and novolac phenol resin (JP-A-5-78552)
Many of the examples mentioned above include in their disclosures a description that the cited product may contain divinylbenzene as a crosslinking agent or a crosslinking auxiliary. This can be attributed to the fact that divinylbenzene has no polar group in its structure and the cured product thereof has a low dielectric constant and low dielectric loss tangent and has a heat decomposition temperature of as high as 350xc2x0 C. or more.
However, divinylbenzene has a defect in that since the cured product thereof is very brittle, cracks tend to develop in the cured product at the time of curing. Therefore, the amount of divinylbenzene added has been usually set at a low level as compared with other resin components.
Even in the example disclosed in JP-A-5-156159 wherein divinylbenzene is used as the main crosslinking agent, the amount added is about 9% by weight relative to the whole of the resin. Divinylnaphthalene also has a problem similar to that of divinylbenzene in point of brittleness of the cured product. Furthermore, since divinylbenzene is volatile, it vaporizes at the time of curing, making it difficult to control the characteristic property of the cured product.
As contrasted therewith, JP-A-5-78552 discloses that such bisstyrene compounds as hydroquinone bis(vinylbenzyl) ether are nonvolatile and can give a highly flexible cured product.
In general, however, an alkylene ether group is disadvantageous with respect to dielectric constant, dielectric loss tangent and heat resistance as compared with an alkylene group and arylene group.
A skeleton of hydrocarbon type, e.g., an alkylene group and arylene group, is preferable as the skeleton structure linking between styrene groups. Examples of a multifunctional styrene compound wherein styrene groups are linked by an ethylene group include 1,2-bisvinylphenylethane described in JP-A-9-208625 and a divinylbenzene oligomer having a vinyl group in the side chain described in Makromol. Chem. Vol. 187, pp 23 (1986). In these reports, however, no investigation was made regarding mechanical strength, heat resistance, dielectric constant and dielectric loss tangent.
Divinylbenzene, which has hitherto been used as a low dielectric constant and low dielectric loss tangent crosslinking agent, is disadvantageous in that it is volatile and its cured product is brittle.
The object of the present invention is to provide a low dielectric loss tangent resin composition containing a crosslinking agent which has a low dielectric constant and low dielectric loss tangent, is excellent in novolatility, solubility and compatibility with various resins and gives a good heat resistance and flexibility after curing, a curable film, a cured product thereof, an electrical part using the same as the insulating material and a method for producing the electrical part.
Some preferred embodiments of the present invention for attaining the above-mentioned object are described below.
(1) A low dielectric loss tangent resin composition containing a crosslinking component having a weight average molecular weight of not more than 1,000 and a plurality of styrene groups and represented by the formula [1]
wherein R is a hydrocarbon skeleton which may have a substituent, R1 is hydrogen, methyl or ethyl, m is an integer of 1 to 4, and n is an integer of 2 or more, and further containing at least one member selected from a high polymer having a weight average molecular weight of not less than 5,000 and a filler;
the low dielectric loss tangent resin composition wherein the high polymer is one having film-forming ability;
the low dielectric loss tangent resin composition which contains a curing catalyst capable of polymerizing and crosslinking the styrene groups or a polymerization inhibitor which can suppress the polymerization and crosslinking of the styrene groups;
the low dielectric loss tangent resin composition wherein the high polymer contains at least one member selected from the group consisting of a homopolymer or copolymer of at least one monomer selected from butadiene, isoprene, styrene, ethylstyrene, divinylbenzene, N-vinylphenylmaleimide, acrylic ester and acrylonitrile, polyphenylene oxide which may have a substituent, polyolefin having a ring structure, polysiloxane and polyether imide;
the low dielectric loss tangent resin composition wherein the filler contains at least one member selected from the group consisting of calcium carbonate, magnesium hydroxide, titanium oxide, silicon oxide, borosilicate glass, aluminum borate and carbon, each having an average particle diameter of 0.1-100 xcexcm;
the low dielectric loss tangent resin composition wherein the amount of the curing catalyst added is preferably 0.0005-10 parts by weight and the amount of the polymerization inhibitor added is preferably 0.0005-5 parts by weight, relative to 100 parts by weight of the whole resin component; and further
the low dielectric loss tangent resin composition wherein the curing catalyst is an organic peroxide or a bisazide compound and the polymerization inhibitor is a quinone or an aromatic diol.
(2) A cured product obtained by curing the above-mentioned low dielectric loss tangent resin composition;
the cured product mentioned above wherein the dielectric loss tangent after curing is preferably not more than 0.002.
(3) A curable film which contains a crosslinking component having a weight average molecular weight of not more than 1,000 and a plurality of styrene groups and represented by the formula [1] and further contains a high polymer having a film-forming ability;
the curable film wherein a conductor layer has been formed on at least one surface of the curable film.
(4) An electrical part having an insulator layer wherein the insulator layer contains a cured product of a low dielectric loss tangent resin composition which contains a crosslinking component having a weight average molecular weight of not more than 1,000 and a plurality of styrene groups and represented by the formula [1] and further contains at least one member selected from a high polymer having a weight average molecular weight of not less than 5,000 and a filler.
(5) A method for producing an electrical part having an insulator layer wherein the insulator layer is a curable film containing a low dielectric loss tangent resin composition which contains a crosslinking component having a weight average molecular weight of not more than 1,000 and a plurality of styrene groups and represented by the formula [1] and further contains a high polymer having film-forming ability, and the curable film is lamination-bonded onto a conductor layer.
It was already described that the cured product of divinylbenzene has a high heat resistance, low dielectric constant and low dielectric loss tangent.
According to the present invention, a cured product which has a low dielectric constant and low dielectric loss tangent and develops no crack at the time of curing could be stably obtained by blending a crosslinking component having plural styrene groups linked with a hydrocarbon skeleton and having a weight average molecular weight of not more than 1,000 with a high polymer having a weight average molecular weight of not less than 5,000 or with a filler.
When a cyclic polyolefin was used as the high polymer component and 1,2-bis(vinylphenyl)ethane as the crosslinking component, the dielectric constant at 10 GHz was 2.19-2.25 and the dielectric loss tangent was 0.0011-0.0017. Since a cyclic polyolefin having no polar group was cured with a crosslinking component having similarly no polar group, a cured product having a low dielectric constant and low dielectric loss tangent was obtained.
Furthermore, since styrene groups are linked by such a flexible skeleton as alkylene group, no cracking occurs at the time of curing.